Is this DS3 or DS4? I recall having an issue like that a time or two in DS3 (or even DS2), but not much in the way of detail. Have you tried saving your work and reopening DS? I've a feeling it may have taken an export to CR2, then reopen in DS to fix.

I am new to rigging, and not only new to rigging, but new to it, using D|S. I had started on a rigging project and had to put it aside for a day or two. Opened my saved scene, and had this very same problem! I rebooted D|S, my computer, tried different settings, nothing worked.

Just tried resaving the CR2, and dropping it back on the "rigging dummy" and voila! Works again!